Process of preparing fibrous esters of cellulose



Patented Mar. 10, 1936 PATENT OFFICE 2,033,716 PROCESS OF PREPARINGFIBROUS ESTERS OF CELLULOSE William 0. Kenyon and George P. Waugh,

Rochester, N. Y., assi Company, Rochester, New York No Drawing. Applicagnors to Eastman Kodak N. Y., a corporation of tion September 8, 1933,

Serial No. 688,623

3 Claims.

The present invention relates to the preparation in fibrous form oforganic acid esters of cellulose, especially mixed organic acid estersin which the cellulose is pretreated with all or substantially all ofthe esterification ingredients except the catalyst, prior to itsesterification.

Heretofore in processes for the preparation of organic acid esters ofcellulose by a fibrous method the cellulose has been pretreated with abath comprising a fatty acid and a catalyst preliminary to itsesterification. Due to the large amount of fatty acid present thepresence of a considerable amount of non-solvent is necessary in theesterification bath to assure non-solution of the ester formed. Thisdisadvantage has been recognized in many cases in which there has beenattempted correction by pressing or centrifuging oil or washing oi? thepretreatment liquid (for instance with non-solvent) which of courseresults in partial removal thereof. This latter procedure permits theuse of less quantities of non-solvent than is the case when the pressingstep is omitted. In some processes for the fibrous preparation ofcellulose esters, probably due to the expense and trouble involved inthe pretreatments ordinarily employed for this type of process, thepretreatment step was omitted entirely, the untreated cellulose beingintroduced directly into the esterification bath. In this latterprocedure the cellulose is not as readily susceptible to esterification,especially in a fibrous esterification process in which the ester is notdissolved upon its formation, as the case where it is pretreated.

One object of our invention is to provide a pretreatment method forcellulose to prepare it for fibrous esterification in which anyappreciable amount of organic acid is unnecessary thus permittingdiminution of the amount of non-solvent ordinarily necessary to preventsolution of the cellulose ester formed. Another object of our inventionis to provide a pretreatment in which substantially all of theesterification mixture except the catalyst is employed to penetrate thecotton so that only the addition of the catalyst is needed to promotethe esterification. Due to the small amount of catalyst necessarycompared to the large amount of conveying liquid which has penetratedthe cellulose the catalyst may readily introduce itself to any portionof the cellulose thus tending toward a uniform action. A further objectof our invention is to provide a pretreatment in which a comparativelylarge amount of pretreating liquid is employed thus assuring thoroughpenetration of the cotton fibers and providing a fluid mass which can,if desired, be

agitated by stirring or be readily flowed from one receptacle toanother.

We have found that an organic acid ester of cellulose may be prepared bya process embodying all the above advantages in which cellulose ispretreated with a mixture of fatty acid anhydride, and an inertnon-solvent and where necessary a small amount of a common solvent suchas propionic or acetic acid to bring all the liquids into mutualsolution. The esterification proper is then brought about by theaddition of catalyst to the pretreatment mass. In the case of somenon-solvents such as those with which the anhydride is compatibleobviously the use of common solvent is unnecessary in the pretreatmentbath. 1

The following examples illustrate fibrous esterification processesembodying our invention:

Example I 20 lbs. of cotton linters were pretreated for approximately 63hours at a temperature of .approximately 40 C. with a mixture comprising30 lbs. of acetic anhydride, 26 lbs. of propionic anhydride, 65 lbs; ofa refined petroleum distillate having a boiling range of -72 C. and 8lbs. of propionic acid. Some of the liquid was pressed off and llb. ofsulfuric acid (sp. gr. 1.84) was added to the pressed off liquid whichwas then remixed with the cotton. 7 35 lbs. more of the petroleumdistillate were added and the whole was maintained at 40 C. for 3 hoursand then at approximately 53 C. for about 20 hours, accompanied byoccasional agitation of the mass. The ester was removed from the bath,washed and dried and exhibited solubilities in the following solvents;ethylene chloride, chloroform, ethylene chloride-ethyl alcohol (90:10)

Example II 20 lbs. of cotton linters were pretreated for about 18 hrs.at 53 C. with a mixture comprising 16 lbs. of propionic anhydride, 36lbs. of acetic anhydride, lbs. of a petroleum distillate having a 60-72C. boiling range and 8 lbs. of propionic acid. Some liquid was separatedoff for instance by draining or pressing and .4 lbs. of sulfuri acid wasmixed therewith whereupon the liquid was again added to the cotton. Thetemperature was raised to 53 C. over a period of about 5 hrs. and wasmaintained at that point for about 18 hrs. The ester was separated outin the manner employed in the previous example. This ester was found toexhibit solubilities similar to those of the product of Example I.

Example III 50 lbs. of cotton linters were pretreated for 16 hrs. atapproximately 53 C. with a mixture comprising lbs. of butyric anhydride,90 lbs. of acetic anhydride, 177 lbs. of a low boiling petroleumdistillate and 22 lbs. of acetic acid. Esterification was induced byadding 1 lb. of sulfuric acid thereto in the same manner as before. Thetemperature was raised to 53 C. over a period of 5 hours and wasmaintained at that point for approximately 18 hours. The product,separated from the reaction mixture in the usual manner, was found to besoluble in ethylene chloride, ethylene chloride-ethyl alcohol (90:10)and chloroform.

Example IV 20 lbs. of cotton linters were pretreated for 16 hrs. at 53C. with a mixture comprising 16 lbs. of propionic anhydride, 36 lbs. ofacetic anhydride and 88 lbs. of benzene. 0.5 lb. of sulfuric acid wasadded in the same manner as in the previous examples and the temperaturewas raised to 53 C. over a period of 5 hrs. and maintained at thattemperature for hours. The product, separated out as before, was solublein ethylene chloride-ethyl alcohol (90:10).

Although our invention is particularly directed to esterificationprocesses in which the saturated aliphatic hydrocarbons, either openchain such as ligroin, gasoline, petroleum ether, and Stoddard Solventdescribed in Bureau of Standards Bulletin, CS3-28, the use of some ofwhich as non-solvents is disclosed in Minsk, Kenyon and Gray applicationSerial No. 671,900 filed May 19, 1933, or cyclic such as cyclohexane,are employed as the non-solvents it will be understood that it is alsoapplicable to esterification processes employing other non-solvents suchas benzene or other aromatic hydrocarbons, carbon tetrachloride or othernon-solvent chlorinated hydrocarbons or higher boiling ethers such asiso-amyl ether, the use of the latter in fibrous esterificationprocesses being disclosed and claimed in Malm and Fletcher Patent No.2,000,602. As was pointed out above when a nonsolvent is employed whichis compatible with the acid anhydride employed, the addition of fattyacid in the pretreatment bath is unnecessary. On the other hand theliquid petroleum hydrocarbons which exhibit the characteristic of incompatibility with acetic anhydride have comparatively high power ofrendering an esterification bath non-solvent of the ester formed so thata smaller quantity thereof is as effective as a greater amount ofanother type of non-solvent. The homogenizing of a fibrousesterification bath in which a petroleum hydrocarbon is employed as thenon-solvent by means of a lower fatty acid is the invention of Minsk,Kenyon and Gray and is disclosed and claimed in their application SerialNo. 671,900, filed May 19, 1933.

Our invention is particularly adapted to the preparation of the lowerfatty acid esters of cellulose such as cellulose acetate, celluloseacetate propionate, cellulose acetate butyrate, cellulose propionate andcellulose butyrate, however, it would obviously follow that it is alsoapplicable generally to the organic acid esters of cellulose.

The esters prepared by our invention may be hydrolyzed to alter theirsolubility properties in any manner designed for the hydrolysis ofcellulose esters in fibrous form, such as for instance in phenol and abasic nitrogen compound which is disclosed and claimed in Staud andMinsk Patent No. 2,000,620 or in a solution of zinc iodide or ferrouschloride in alcohol which process is disclosed and claimed in Staud andMurray Patent No. 2,005,383. By this hydrolysis step an ester such asprimary cellulose acetate which is acetone-insoluble may be converted tothe acetone soluble variety.

There are many catalysts which will promote the esterification ofcellulose known in the art and it is to be understood that one of thesemay be employed in our invention instead of sulfuric acid which wasemployed in the processes disclosed in the examples.

We claim as our invention:

1. A process for preparing an organic acid ester of cellulose in fibrousform which comprises pretreating the cellulose, in the absence of acatalyst, with a mixture comprising a lower fatty acid anhydride, aliquid petroleum distillate which is essentially within a boiling rangeof 40-210" C. as the non-solvent for the ester to be formed and a lowerfatty acid to homogenize the mixture, and thereafter causingesterification by adding a catalyst to the mass.

2. A process for preparing an organic acid ester of cellulose in fibrousform which comprises pretreating the cellulose in the absence of acatalyst with a mixture comprising a lower fatty acid anhydride, aliquid petroleum distillate which is essentially within a boiling rangeof 40-210 C. as the non-solvent for the ester to be formed and propionicacid to homogenize the mixture, and thereafter causing esterification byadding a catalyst to the mass.

3. A process for preparing an organic acid ester in fibrous form whichcomprises pretreating the cellulose in the absence of a catalyst with amixture comprising acetic anhydride, a liquid petroleum distillate whichis essentially within a boiling range of 40-210 C. as the non-solventfor the ester to be formed and a lower fatty acid to homogenize themixture and thereafter causing esterification by adding a catalyst tothe mass.

WILLIAM O. KENYON. GEORGE P. WAUGH.

